Introduce client-side localization helper and en/fr locale bundles.
Route admin control, picks, movies, stats, winners and settings UIs through i18n keys instead of hardcoded text.
Remove French text from the English UI and standardize shared messages (saving, network errors, confirmations).
Update .gitignore to ignore editor metadata and localization helper artifacts.
Persist last applied theme in session storage to avoid light-mode flash and toggle flicker when navigating between pages (notably player.html). Also revert README preview back to preview.png for now.